The present invention relates to a magnetic tape cassette, particularly, to a magnetic tape cassette used in a VTR (video tape recorder) or the like.
A variety of magnetic tape cassettes, including those of the Beta and VHS type, are known for use in VTRs or the like. The conventional cassettes all employ the same basic structure. FIG. 1 shows, as an example, a cassette of the VHS type. The magnetic tape cassette of FIG. 1 includes a tape guiding structure such as cylindrical tape guides 13, a guide pole 14, a guide roller 15, and a pressure pad 16 which cooperate to guide a magnetic tape T in running between a supply reel 11 and a take-up reel 12.
The sliding characteristics of the magnetic tape on these guide members greatly affect the tape running characteristics. This can be readily understood from the fact that the magnet tape T is manufactured by forming a magnetic layer on a flexible film support made of acetate, polyester, or vinyl chloride, as is well known in the art. To increase the total recording and playing time of the tape, or to improve the electromagnetic properties of the tape, a thinner tape having a high surface smoothness has been developed.
To take advantage of the improved sliding properties of such a tape, it is necessary to improve the surface smoothness of the above guide members. That is, as the thickness of the magnetic tape is reduced, its rigidity is decreased, and therefore the running characteristics of the tape are more strongly affected by the guide members. In the case of a tape used for recording and reproducing data at a high recording density, even slight variations in the behavior of the magnetic tape can strongly affect the recording and reproducing operations carried out with the tape. For example, variations in the behavior of the tape running can result in a jitter phenomenon, making the reproduced picture waver in the horizontal direction. Accordingly, it is essential to make the tape run smoothly.
The inventors have conducted intensive research into the above-described problems and found that variations in the running characteristics of the tape are largely attributable to the guide members which are in contact with the magnetic layer of the tape, namely, the guide pole 14 as shown in the example of FIG. 1, and to the surface characteristics of the tape itself. For instance, a tape with a magnetic surface having an Ra value of less than 0.01 .mu.m (cut-off value of 0.25 mm) is more likely to have adversely affected tape running characteristics.
Thus, the above-described drawbacks may be eliminated with the provision of a guide pole 14 (with which the surface of the magnetic layer of the tape is brought into contact) which is made harder than a conventional guide pole and which is polished or subjected to other surface treatment so as to improve its surface smoothness. On the other hand, such techniques significantly increase the manufacturing cost of the guide pole, making the guide pole impractical for ordinary manufacturing use.